Ramsey Electronics SG560 Guía de usuario descargar pdf (Pagina 53)

TYPICAL TEST PROCEDURES

3.20.08 Tuning a duplexer

The three types of duplexers commonly used in VHF, UHF and 800 MHz communication

systems are:

1. Band Pass

2. Band Pass-Band Reject

3. Band Reject

The COM 3010, with its high stability accurate signal source and the associated RSSI receiver,

makes accurate duplexer testing and retuning fast and easy.

This tuning procedure deals specifically with the Band Reject type, square or round cavity

design. Check the manufacturer’s specifications to make sure that you are tuning a Band

Reject duplexer.

IMPORTANT NOTES:

Be sure the cables used for duplexer testing are of high quality double shielded type with

the proper connectors. BNC-N and BNC-BNC, RG 142 cables from Pasternack.com are a

good solution.

Before starting the tuning procedure make sure you calibrate the RSSI indicator to the

generator output.

You will be adjusting only the tuning rods or screws.

The lock nuts on the tuning knob adjustment shafts should be loosened to allow the

tuning shafts to be adjusted smoothly. Be aware that tuning is slightly affected as the lock

nuts are tightened down and it will likely be necessary to readjust each notch as the lock

is slowly tightened.

The Generator output should read -dbm

The Receiver input should read RSSI –dbm

Record the repeater Transmit and Receive frequencies and determine the high side, low

side and calculate the frequency separation. For Example, 466.500 MHz repeater receive

and 461.500 repeater transmit = 5 MHz separation.

The receiver side of the duplexer will be tuned to reject (notch) the transmitter frequency

and it will be the most critical adjustment to make. This adjustment makes sure there is

high isolation from the transmitter to the receiver.

The transmit side of the duplexer will be tuned to reject (notch) the receiver frequency.

This adjustment assures high isolation from the transmitter to the receiver.

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Ramsey Electronics SG560 Guía de usuario Pagina 53